The Otto and Diesel internal-combustion engines have existed for over 100 years. These types of internal-combustion engines have many advantages and some disadvantages, including considerable vibration, many moving parts, a large number of parts that are subject to failure, and difficulties in making repairs, since many of these parts are embedded inside these complex engines.
In Wankel-type rotary engines, reciprocating pistons are replaced by rotors that orbit eccentrically around a center axis. The rotor in the Wankel-type engine is triangularly shaped and rotates within a surrounding chamber. The Wankel-type engine is simple and has a small number of moving parts. The disadvantages are that very high friction is created, which results in high wear, inefficiency, frequent failure, and limited rotational speed and power.